Effect of imidazole on oxytocin and acetylcholine induced responses in isolated rat uterus: with observations on its mechanism of action.

Imidazole (3.67 x 10(-3) M) and sodium bicarbonate (1.78 x 10(-2) M) failed to alter acetylcholine evoked responses in isolated rat uterus but they produced a significant shift of the log dose-response curve of oxytocin to the left. This potentiating effect was reversible. Addition of imidazole increased the pH of de Jalon solution from 7.2 to 8.5. Sodium dihydrogen orthophosphate (3.3 x 10(-3) M) prevented the change of pH due to the addition of imidazole and at the same time the potentiating effect of imidazole was inhibited. The present study strongly suggests that the potentiation of oxytocin-evoked responses by imidazole is due to the change in pH of de Jalon solution towards more alkaline range and it may not be due to stimulation of phosphodiesterase activity of rat uterus.